Wednesday, November 26, 2014

The non-titanosauriform macronarian Camarasaurus is one of the American public's favorite macronarian sauropods from the Jurassic, being thought of as the most common macronarian from the Morrison Formation. Very few sauropod workers, however, have tackled the alpha-taxonomy of the genus and its various constituent taxonomy since the papers by Ikejiri (2005) and Osborn and Mook (1921). The result has been the tendency to treat Camarasaurus as a genus in numerous phylogenies of Sauropoda (Upchurch et al. 2004; Wilson 2002) without a comprehensive analysis of intrageneric variation of the genus.In recent abstracts published at the SVP 2013 and 2014 meetings, Mateus and Tschopp (2013) and Tschopp et al. (2014) work to address the question of intraspecific variation in Camarasaurus. The abstract by Mateus and Tschopp (2013) deals with a newly discovered camarasaurid (SMA 0002) that is referred to Cathetosaurus lewisi based on shared characters with BYU 9047 (holotype of C. lewisi). On the other hand,Tschopp et al. (2013) conduct a specimen-level analysis of all Camarasaurus specimens including the type specimens of currently recognized species of the genus (C. grandis, C. lentus, and C. supremus). The phylogenetic results reported by Tschopp et al. (2014) seem to not only reaffirm the distinctness of Cathetosaurus from Camarasaurus, but they also support the validity of the three historical species of the latter genus.These preliminary results have prompted me to revisit the synonymy of Caulodon with Camarasaurus performed by Osborn and Mook (1921) and followed by subsequent authors. When placing the two nominal species of Caulodon (C. diversidens and C. leptoganus)in synonymy with Camarasaurus supremus, Osborn and Mook noted that AMNH 5768 and AMNH 5769 were similar to the maxillary teeth of a referred specimen of Camarasaurus supremus (AMNH 5761) in being robust and spatulate-shaped, but were hesitant to rule out the possibility of two different sauropods with spatulate teeth from the Morrison Formation. However, they did not compare the holotypes of Caulodon diversidens and C. leptoganus with the teeth of Giraffatitan or USNM 5730 (referred to Brachiosaurus sp. by Carpenter and Tidwell 1998).

Since the monograph by Osborn and Mook, robust spatulate teeth have been described for numerous non-neosauropod and macronarian sauropods, including USNM 5730, Europasaurus, Mamenchisaurus, Turiasaurus, and Jobaria (Carpenter and Tidwell, 1998; Marpmann et al. 2014; Ouyang and He 2002; Royo-Torres and Upchurch 2012; Russell and Zheng 1994; Sereno et al. 1999). Because robust spatulate teeth are no longer considered diagnostic for Camarasaurus supremus or other camarasaurid species and are widely distributed among non-neosauropod and non-titanosauriform sauropods, Caulodon and its nominal species should not be considered synonymous with Camarasaurus supremus and instead must be considered nomina dubia at Eusauropoda indeterminate.
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Sunday, September 7, 2014

Ever since the 1980s, many dinosaurologists familiar with sauropods have become fascinated by the specter of extravagantly colossal sauropod species, fortified by the discoveries of the giant diplodocids Seismosaurus hallorum (now Diplodocus hallorum) and Supersaurus vivianae in the 1970s and 1980s. When James Jensen announced the discovery of Supersaurus and its junior synonym Ultrasauros, the mainstream media outlets hailed Ultrasauros as the largest and heaviest sauropod that ever lived, and based on the holotype (BYU 9044) and the brachiosaurid scapulocoracoid BYU 9462, Jim Jensen put the estimates of the length and weight of Ultrasauros at 80 to 100 feet long (25 to 30 meters) and 75 tons (75,000 kilograms) respectively. On the other hand, the discoverer of Diplodocus hallorum, David Gillette, estimated the maximum length and weight of D. hallorum at 177 feet long (54 meters) and 125 tons (113,000 kilograms) respectively. However, the giant Morrison sauropods were eclipsed by the Patagonian titanosaurs as regards discussion of the heaviest sauropod taxa, and recent publications (Carpenter 2006; Foster 2003) have put Diplodocus hallorum and Supersaurus vivianae in the 33 to 50 ton range (30,000 to 45,000 kilograms), a far cry from the earlier weight estimates.Now, the media has seized upon the discovery of the latest giant titanosaur to be described, Dreadnoughtus schrani (Lacovara et al. 2014), by hailing it as probably the biggest and heaviest sauropod ever to have roamed the earth. This discovery has provided a new window into the question of which sauropod was the heaviest that ever lived, but to compare Dreadnoughtus against other contenders for the title of heaviest sauropod (Argentinosaurus, Futalognkosaurus, Puertasaurus), I have the opportunity to discuss various weight and size estimates for the giant Patagonian titanosaurs with respect to Equation 1 devised by Campione and Evans (2012), which extrapolates the weight of a quadrupedal animal from the minimum circumference of the shaft of its humerus and femur.When using Equation 1 of Campione and Evans (2012) in order to calculate the body mass of Dreadnoughtus, Lacovara et al. (2014) put the body mass estimate of this genus at 65.4 tons (59,291 kilograms), while noting that the body mass of Dreadnoughtus was probably greater taking into account their histological analysis indicating that the holotype (MPM-PV 1156) was not yet fully grown but still massive in terms of body mass. This is well above the weight estimates provided for Giraffatitan brancai by Benson et al. (2014) but less than the body mass estimate of 134.9 tons (122,400 kilograms) provided for the diplodocoid "Amphicoelias" fragillimus by Carpenter (2006), and less than the weight estimated by Mazetta et al. (2004) for the titanosaur "Antarctosaurus" giganteus. (Since the holotype remains of "Amphicoelias" fragillimus [AMNH 5777] have been lost, it is possible that Carpenter's weight estimate for this species is way off by several tons and "A." fragillimus was not as heavy as estimated by Carpenter.) By contrast, the primitive titanosaur Futalognkosaurus and the turiasaur Turiasaurus weighed 42 tons (38,139 kilograms) and 56.1 tons (50,923 kilograms) respectively.

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Regarding the body mass of Argentinosaurus, Paul (1994) put the weight estimate of Argentinosaurus at 88 to 110 tons (80,000 to 100,000 kilograms), but Mazzetta et al. (2004) revised the weight to 80 tons (73,000 kilograms), while Sellers et al. (2013) put the weight estimate at 91 tons (83,000 kilograms). Although it is not implausible that Argentinosaurus was bigger and heavier than Dreadnoughtus judging from the size of the referred femur (MLP-DP 46-VIII-21-3), the known material of Argentinosaurus comprises only a tiny part of the postcranial skeleton (9.2 percent), insufficient to give a reliable estimate of the body mass of Argentinosaurus using the body mass formula devised by Campione and Evans (2012). Likewise, another giant titanosaur from Patagonia, Puertasaurus, may have been heavier and bigger than Dreadnoughtus, with an estimated weight of 88 to 110 tons (80,000 to 100,000 kilograms) based on the huge size of the dorsal vertebra (Novas et al. 2005), but the available material is too meagre to give a more accurate body mass estimate and more complete remains are needed to determine the size of Puertasaurus. In summary, any possible body mass estimates for "Amphicoelias" fragillimus, Argentinosaurus, and Puertasaurus should be treated with caution when taking these sauropods as candidates for the title of heaviest sauropod. Since "Antarctosaurus" giganteus has femora preserved in its type material, it could be a viable contender for the title of heaviest sauropod. Therefore, it may be parsimonious to treat "A." giganteus and Dreadnoughtus as the heaviest sauropods known to science given that the holotype of the former species was not yet fully mature. Update: A new paper by Bates et al. (2015) suggests that the original weight estimate for Dreadnoughtus was an overestimate and that Dreadnoughtus probably weighed 42.1 tons (38,225 kilograms), rather than 65.4 tons as originally claimed by Lacovara et al. (2014).Benson RBJ, Campione NE, Carrano MT, Mannion PD, Sullivan C, et al., 2014. Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biol 12(5): e1001853 doi:10.1371/journal.pbio.1001853.

Campione, N., and Evans, D., 2012. A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods". BMC Biology: 15. doi:10.1186/1741-7007-10-60.Carpenter, K., 2006. Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus. In Foster, John R.; and Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36. Albuquerque: New Mexico Museum of Natural History and Science. pp. 131–138.

Thursday, May 29, 2014

In part 1 of my review of the McPhee et al. (2014) paper on the osteology of the basal sauropod Antetonitrus, I discussed the definition of Sauropodiformes and Sauropoda within in the context of the analysis by McPhee et al. (2014) regarding Antetonitrus. However, one overlooked aspect of the paper that didn't make anyone notice it was the discussion of the possible affinity of the Maphutseng sauropodomorph (aka "Thotobolosaurus") with Antetonitrus on page 157 of the paper.The Maphutseng sauropodomorph, like the Proctor Lake hypsilophodont and the Dalton Wells quarry iguanodont, has been occasionally mentioned in the literature but has been only briefly described. It was first reported by Ellenberger and Ellenberger (1956) based on sauropodomorph remains pertaining to a minimum of six individuals collected from from the Late Triassic lower Elliot Formation of Maphutseng, Lesotho in the 1950s. The Maphutseng taxon was discussed by Charig et al. (1965), Ellenberger (1970), and Ellenberger & Ginsburg (1966), who noted its affinities with sauropods relative to other "prosauropods"; Ellenberger (1970) coined the nomen nudum "Thotobolosaurus mabeatae"for the Maphutseng sauropodomorph in his discussion of the fossil record of southern Africa for the Triassic-early Jurassic interval, but never described it in detail. Gauffre (1993) preliminarily re-assessed the Maphutseng sauropodomorph and tentatively referred it to the nomen dubium Euskelosaurus browni, but he later (1996) changed his mind about the attribution of this taxon and described it as a distinct sauropodomorph under the nomen ex dissertationae "Kholumolumosaurus ellenbergerorum".

The remains of "Thotobolosaurus"/"Kholumolumosaurus" being excavated in Maphutseng, Lesotho.

Note: Since this post was published, it has become clear (Peyre de Fabregues and Allain 2016) that Antetonitrus is not from the lower Elliot Formation as previously thought, but instead from the upper Elliot Formation, meaning that the Maphutseng sauropodomorph is clearly not congeneric with Antetonitrus.

Charig, A.J., Attridge, J.& Crompton, A.W. 1965.On the origin of the sauropods and the classification of the Saurischia. Proceedings of the Linnean Society 176: 197–221.

F.-X. Gauffre. 1993. Biochronostratigraphy of the lower Elliot Formation (southern Africa) and preliminary results on the Maphutseng dinosaur (Saurischia: Prosauropoda) from the same formation of Lesotho. In S. G. Lucas and M. Morales (eds.), The Nonmarine Triassic. New Mexico Museum of Natural History and Science Bulletin 3:147-149.

Wednesday, May 7, 2014

In a paper describing the anatomy of the primitive Triassic sauropod Antetonitrus ingenipes, McPhee et al. (2014) define the clade Sauropodiformes as including all sauropodomorphs more closely related to Sauropoda than to Massospondylus or Plateosaurus, and they slightly retreat from the original systematic placement of Antetonitrus in Sauropoda by treating it as a sauropodiform close to, if not, part of Sauropoda. However, while McPhee et al. summarize the importance of Antetonitrus in highlighting the transition from the sturdy massospondylids and plateosaurids to the bulky and massive sauropods, the use of the definition of Sauropoda sensu Salgado et al. (1997) by the authors should be taken with a grain of salt.With respect to the cladistic analysis of Sauropod by McPhee et al. (2014), exclusion of Antetonitrus and Lessemsaurus from Sauropoda would render the sauropod clade Gravisauria Allain and Aquesbi, 2008 synonymous with the definition of Sauropoda sensu Salgado et al. (1997). However, Otero and Pol (2013) treat Antetonitrus, Blikanasaurus, and Lessemsaurus as sauropods under the definition of Sauropoda articulated by Allain and Aquesbi (2008), so it makes sense to retain the sauropod classification of Antetonitrus to avoid creating tiresome phylogenetic clade names in future cladistic analyses of basal sauropods because the Early Jurassic sauropodiform Aardonyx is more primitive than the only other non-sauropod sauropodiform clade from southern Africa, Melanorosauridae.Irrespective of definition of Sauropoda offered by either McPhee et al. (2014) or Allain and Aquesbi (2008), I have decided to straddle the fence and treat Antetonitrus as a true sauropod just for the sake of phylogenetic accuracy and robustness. Allain, R. and Aquesbi, N., 2008. Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas 30(2): 345-424.McPhee, B. W., Yates, A. M., Choiniere, J. N. and Abdala, F., 2014. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda. Zoological Journal of the Linnean Society, 171: 151–205. doi: 10.1111/zoj.12127Otero, A.; Pol, D., 2013. Postcranial anatomy and phylogenetic relationships ofMussaurus patagonicus (Dinosauria, Sauropodomorpha). Journal of Vertebrate Paleontology33 (5): 1138-1168. doi:10.1080/02724634.2013.769444.edit

Tuesday, April 15, 2014

In a paper discussing ontogeny in the neck vertebrae of diplodocids, Woodruff and Fowler (2012) questioned the validity of Suuwassea emilieae and its placement in Dicraeosauridae. For example, they noted that several characters used to place the genus in Dicraeosauridae (tall cervical neural spines and an anterior prominence at the dentary symphysis) are either symplesiomorphic or also found in the juvenile specimen MOR 592 (referred to Amphicoelias sp. by Wilson and Smith 1996). Moreover, the lack of scapulocoracoidal fusion, the slight bifurcation of the cervical neural spines, and the elongation of the foot bones are used by the authors to point to the immature growth status of ANSP 21122. Therefore, Woodruff and Fowler concluded that Suuwassea might be a possible juvenile form of one of other diplodocoids from the Late Jurassic Morrison Formation.Although ontogeny could explain some of the non-diplodocid characters in Suuwassea, it is important to note several things. First, the postparietal foramen used to place Suuwassea in Dicraeosauridae is also found in the diplodocine diplodocid Kaatedocus siberi (Tschopp and Mateus 2013) and the indeterminate flagellicaudatan braincase MB.R.2387 (Remes 2009). Other putative dicraeosaurid synapomorphies of Suuwassea listed by Whitlock (2011) (sharp sagittal crest on supraoccipital) are also present in Kaatedocus. Given the diplodocid placement of Kaatedocus and the uncertain status of MB.R.2387 within Flagellicaudata, the presence of a postparietal foramen in both Suuwassea and Kaatedocus appears to be a case of convergent evolution because, as pointed by Tschopp and Mateus, the diplodocid Diplodocusskull CM 11255 lacks such a foramen and Suuwassea and Dicraeosaurus have a postparietal foramen smaller than that of Kaatedocus and MB.R.2387.Even if the holotype of Suuwassea were subadult, it would still be a distinct species judging from available evidence above. It may take future discoveries to confirm or refute the hypothesis by Woodruff and Fowler (2012) regarding the validity of Suuwassea.Update: The landmark revision of Morrison diplodocid alpha-taxonomy by Tschopp et al. (2015) indicates that some putative dicraeosaurid characters of Suuwassea (postparietal foramen, sharp sagittal crest on supraoccipital) are also found in the diplodocid Galeamopus, but recovers Suuwassea as dicraeosaurid.

Emanuel Tschopp & Octávio Mateus, 2013. The skull and neck of a new flagellicaudatan sauropod from the Morrison Formation and its implication for the evolution and ontogeny of diplodocid dinosaurs. Journal of Systematic Palaeontology11 (7): 853-888, DOI: 10.1080/14772019.2012.746589

Wednesday, February 19, 2014

It's been barely a year since the second of the three Jurassic Portuguese sauropods, the brachiosaurid titanosauriform Lusotitan ataialensis, was put in a cladistic context by Mannion et. al. (2013). Now, Mocho et. al. (2014) have published a paper re-assessing the cladistic position of the third described Portuguese sauropod, Lourinhasaurus alenquerensis, following in the footsteps of Mannion et. al. (2012, 2013) in putting all of Portugal's sauropod taxa in a phylogenetic context.As we all know, Lourinhasaurus was originally assigned to Apatosaurus by Lapparent and Zbyszewski (1957) and later referred to Camarasaurus by McIntosh (1990). However, Dantas et. al. (1998) removed alenquerensis from Camarasaurus and assigned it to a new genus Lourinhasaurus. Because the original description of this taxon had a rather inadequate diagnosis, Upchurch et. al. (2004) found it to be in an unstable position in Eusauropoda.When browsing through the supplementary material for Mocho et. al. (2014), it's interesting that while the cladistic analyses both recover a monophyletic Camarasauridae formed by Camarasaurus, Lourinhasaurus, and Tehuelchesaurus, they treat nemegtosaurids as diplodocoids rather than titanosaurs and Haplocanthosaurus as a macronarian rather than a diplodocoid, while failing to support a monophyletic Euhelopodidae sensu D'Emic (2012). However, this is likely due to the failure of Mocho et. al. (2014) to incorporate characters from the cladistic analyses of D'Emic (2012) and Whitlock (2011).